Perfect Tube Research Articles

Structure and electrical properties of double-walled silicon nanotubes depending on 585 defects and applied electric fields by SCC-DFTB method

The geometric structural and electronic properties of 585 defective double-walled silicon nanotubes (DWSiNTs) by using the self-consistent charge density functional tight-binding (SCC-DFTB) method. Furthermore, we investigated the impact of external electric field and intensity on the electronic properties. After the relaxation of perfect tubes, the structure of the tube changes significantly, and the winding direction of the tube wall changes. The buckling value of the tube wall is most closely related to the geometric shape and atomic arrangement order of tubes. The overall stability of zigzag tubes is higher than armchair tubes, and (6,6)@(10,10) stability is significantly affected by defects. The partially defected zigzag tubes change from direct band gap semiconductor properties to indirect band gap semi-metal properties. A transformation of the semiconductor-semimetal properties, direct-indirect band gap of DWSiNTs is realized. The charge transfer amplitude of the defect tubes is greater than the perfect tube. The applied electric field makes the stability of all tubes decrease linearly, and the stability of the defect tubes is higher than the perfect tube. Part of the electric field strength changes the defect tubes from semiconductor properties to semi-metal properties, and semi-metal properties to metal properties. These theoretical studies provide a reference for the preparation and future application of DWSiNTs.

Variation in properties of double-walled zigzag and armchair silicon nanotubes depending on SW defects and applied electric fields by SCC-DFTB method

The geometric structure and electrical properties of the zigzag DWSiNT (8,0)@(12,0) and armchair DWSiNT (5,5)@(7,7) perfect tubes with the same diameter are simulated by self-consistent charge density functional tight binding method (SCC-DFTB). We considered the defective tubes by introducing three types of Stone-Wales (SW) defects, and further investigated the impact of both strong and weak electric fields on these defective tubes. Calculations demonstrate that the atomic arrangement regularity, degree of buckling, stability, energy gap, and charge distribution strongly depend on the type of perfect tubes. Following the introduction of the SW defects, the symmetry of the tubes disappeared, and there is a obvious atomic aggregation occurring at the defects. The armchair tubes demonstrate a higher stability compared to zigzag tubes and all exhibit metallic properties. SWⅡ and SWⅢ defects in zigzag tubes result in a transition from semiconductor to semi-metallic properties. The number of charge transfer increases, and the degree of atomic aggregation is more dispersed. The effect of applied electric field strength on perfect zigzag tubes is more obvious. The weak field has minimally impacted on the stability, and the strong field makes the stability improved to some extent. The presence of a strong field caused the energy gap values of (8,0)@(12,0) tube decrease sharply, and all tubes are transformed into semi-metal or metal. The weak electric field has a more pronounced regulation of band gap within the range of 0 V/nm - 0.3 V/nm on the inner tube. The consequences of this investigation can certainly be helpful in future experimental studies.

Effects of Stone-Wales defects on structure and electrical properties of double-walled silicon nanotubes by SCC-DFTB method

In this work, the geometric structure, system stability, electrical properties and charge distribution of zigzag double-walled silicon nanotubes (DWSiNTs) (nin,0)@(nout,0) (nin = 5–7, nout = 8–13) perfect tubes and defective tubes with three types of Stone-Wales (SW) defects were studied using the self-consistent charge density functional tight-binding (SCC-DFTB) method. The change of the chirality index between the inner and outer walls was simulated. The results show that the symmetry of the structure disappears, and the warping of the tube wall changes from order to disorder after introducing SW defects. The warps of outer tube are obviously higher than that of inner tube. The perfect tubes with inner wall chirality index (6,0) are more stable than other tubes. SW defects of outer wall tubes have a higher effect on system stability than those of inner wall tubes. The difference of inner and outer wall chirality indices plays an obvious role in regulating the energy gap of the system, half of which are near-metal properties and the other half semiconductor properties, and the regulation range is 0.1075–0.8519 eV. All types of SW defects at all locations have a certain regulatory effect on the energy gap of DWSiNTs, and the effect of type III defect is the most obvious. The effect of atomic charge redistribution in the tube is related to the structure, and the charge transfer in a perfect tube is symmetrical. The number of electrons obtained at the defect is increased, and the electronegativity is stronger, due to the curvature of local atoms produced at the defect. This study provides a reference for the preparation and future application of DWSiNTs.

Predicting the wrinkling in AA5052 seamless tubes manufactured by free bending forming technology

Wrinkling is a significant defect during forming of thin-walled metallic tubes via free-bending forming (FBF) technology. Thus, it's quite important to predict the wrinkling in the tubes to improve the quality of the final products. Accordingly, new theoretical and numerical frameworks were proposed for predicting the wrinkling of the tubes manufactured via FBF technology. The theoretical wrinkling prediction model is based on the energy criteria and the thin shell theory. The numerical prediction model was constructed on the ABAQUS/Implicit FE code. Besides, The Knoop microhardness test characterized the anisotropy of the tube. The tube's imperfection was introduced to the numerical model through pure bending buckling analysis. The bending experiments were conducted to verify the results obtained from the proposed theoretical and numerical frameworks and showed good agreement with them. Furthermore, it was noticed that the additional axial force in the FBF process reduces the tube's ability to resist wrinkles. The larger additional axial force makes tubes more sensitive to imperfection in free bending than in other bending technologies. The numerical prediction model with the perfect tube exhibits good accuracy in predicting the initiation of the tube wrinkling in free bending but not in terms of the wrinkling shape. The model considering the imperfection can predict the onset and development of wrinkling properly.

Highly active MIL-68(In)-derived In2O3 hollow tubes catalysts to boost CO2 hydrogenation to methanol

MIL-68(In)-derived In2O3 hollow tubes with different morphology and size using MIL-68(In) as a template were prepared at different NaOAc concentrations and applied to CO2 hydrogenation to methanol. The size of a series of MIL-68(In) gradually decreased with increasing NaOAc concentration. Too large or small diameter of MIL-68(In) (NaOAc at 0.2 M or 1 M) led to the collapse of corresponding derivative In2O3 tubular structure and only haphazardly accumulated In2O3 nanoparticles were retained. However, the In2O3 hollow tubular-like structure could be obtained when NaOAc concentrations were in the range of 0.4 M to 0.65 M. Interestingly, the self-assembly MIL-68(In)-0.5 M-derived In2O3 with the most regular and perfect hollow tube structure was composed of ordered arrangement of In2O3 nanoparticles at 0.5 M NaOAc, which exhibited much higher methanol synthesis performance than that of other In2O3 catalysts. The lowest surface reduction temperature led to oxygen vacancies easily exposed on In2O3-0.5 M hollow tube surface. The space confinement effect further enhanced the reaction efficiency of oxygen vacancies, and adsorption capacity of CO2 was enhanced to improve the methanol yield. It achieved a CO2 conversion of 14.0%, while methanol selectivity remained at 65%. The space-time yield was up to 1.07 gMeOHh-1gcat-1, showing excellent methanol activity.

The structure and properties of a carbon nanotube (7, 7) with a vacancy defect

Carbon nanotubes (CNTs) still draw great attention of researchers due to their possible use as anodes for lithium-ion batteries. The capacity of the anode for lithium ions is defined by the efficiency of diffusion of these ions to the adsorption centers located on the outer or inner surface of the nanotubes, as well as between the layers of multi-walled nanotubes. The inner surface can be accessed through the open ends of the tubes or defects in their frame. Moreover, the defects create more efficient adsorption sites than the surface of a perfect tube. This work presents the results of the ab-initio modeling of the lithium adsorption on a carbon nanotube (7, 7) with a vacancy-type defect. The simulation was carried out using density functional theory implemented in the SIESTA package. The Ceperley-Alder exchange-correlation functional and the DZP basis set were used. The formation energies of vacancy defects of two types were determined. Additionally, for each vacancy type, the binding energies of lithium atoms adsorbed inside and outside the CNT (7, 7) near the defect were calculated. These binding energies were shown to be up to twice bigger than on a perfect CNT. The enhancing effect of the vacancy on the CNT sorption activity was found to be wide-ranged: it was observed for adsorption sites in the first and second surroundings of the defect and even for sites located on the tube surface opposite to the defect.

Sensing and monitoring of edifenphos molecules based on the quantum chemical approach.

The tendency of edifenphos (EDF) species toward boron carbide nanotube (BC3NT) was investigated through density functional theory (DFT) calculations with perfect and defected forms. It was found that perfect BC3NT tube is not capable to adsorb the EDF molecules appropriately. Introducing defects in BC3NT lattice resulted in a noticeable enhancement of interaction with EDF providing the adsorption energy of - 25.66kcal/mol. It was predicted that the conductivity of complex formed of single vacancy BC3NT tube, SV-BC3NT, and EDF complexes is enhanced by 91.37 times compared with BC3NT tube with no defects. As the solvent dielectric constant increases, a significant change in adsorption energy was reported while slighter variation was observed at dielectric constant values lower than 15. Similar to electric conductivity, the magnetic properties of BC3NT are remarkably enhanced after single vacancy defect and EDF adsorption leads to a highly significant change in magnetic property compared with perfect BC3NT. Graphical abstract.

Limit load analysis and imperfection sensitivity of porous FG micro-tubes surrounded by a nonlinear softening elastic medium

An imperfection sensitivity analysis for the nonlinear post-buckling behavior of functionally graded (FG) porous micro-tubes is performed in this research. The case of geometrically imperfect micro-tubes surrounded by a nonlinear elastic medium under axial compressive load is analyzed. Properties of the micro-tube with uniform distributed porosity are FG across the radius of the cross-section. Two types of boundary conditions as simply-supported and clamped are considered. The high-order shear deformation theory of tubes is utilized to approximate the displacement field. Differential equations governing the equilibrium position of the micro-tube are extracted using the virtual displacement principle. These nonlinear equations are analytically solved by means of the two-step perturbation technique and Galerkin procedure. It is shown that when the imperfect micro-tube is in contact with a sufficiently soft foundation, the post-buckling path of the structure is unstable, and therefore the structure is imperfection sensitive. Since the imperfection sensitivity of micro-tubes is not reported in literature, results of this study are compared with buckling responses of perfect FGM tubes. The effects of porosity coefficient, power law index, length scale parameter, and geometrical parameters upon the limit buckling load of imperfect micro-tubes are investigated.

Electronic Structure of WS2 Nanotubes—Potential Catalysts of Water Photolysis

The band structures of (15, 10), (21, 0), (16, 8), (18, 6), and (12, 12) WS2 nanotubes of various chirality and diameter have been calculated by the linearized augmented cylindrical wave method in order to elucidate the extent to which they meet the requirement for sunlight water splitting catalysts. It is expected that the introduction of impurities and structural defects should increase the activity of the photocatalyst as compared with perfect tubes.

Electronic and transport properties of zigzag carbon nanotubes with the presence of periodical antidot and boron/nitride doping defects

Electronic and transport properties of Carbon nanotubes (CNTs) are affected by the presence of physical or chemical defects in their structures. In this paper, we present novel platforms of defected zigzag CNTs (Z-CNTs) in which two topologies of antidot and Boron/Nitride (BN) doping defects are periodically imposed throughout the length of perfect tubes. Using the tight binding model and the non-equilibrium Green’s function method, it is realized that the quantum confinement of Z-CNTs is modified by the presence of such defects. This new quantum confinement results in the appearance of mini bands and mini gaps in the transmission spectra, as well as a modified band structure and band gap size. The modified band gap could be either larger or smaller than the intrinsic band gap of a perfect tube, which is determined by the category of Z-CNT. The in-depth analysis shows that the size of the modified band gap is the function of several factors consisting of: the radii of tube (Dr), the distance between adjacent defects (dd), the utilized defect topology, and the kind of defect (antidot or BN doping). Furthermore, taking advantage of the tunable band gap size of Z-CNT with the presence of periodical defects, new platforms of defect-based Z-CNT resonant tunneling diode (RTD) are proposed for the first time. Our calculations demonstrate the apparition of resonances in transmission spectra and the negative differential resistance in the I-V characteristics for such RTD platforms.

Obtaining global equations for the Young’s modulus of perfect and defective carbon nanotubes

There are limited studies which have extracted global equations for calculation of Young’s modulus (E) in both pristine and defective carbon nanotubes (CNT), especially when a combination of different defects such as atom-vacancy and-misplacement exist simultaneously in the studied CNT. In this study, the finite element method was used to investigate E for a large set of perfect and defective single walled carbon nanotubes (2440 finite element models), including armchair, zigzag and chiral tubes. The obtained results were then employed as the basis for achieving accurate global equations for calculation of E in perfect and defective carbon nanotubes at various defect percentages. Despite most previous studies, which were based on the tube’s diameter, the chiral indices (n, m) have been considered here as variables to predict the stiffness of carbon nanotubes. The achieved equations showed to be accurate, with maximum errors below 2% and 10% for perfect and defective tubes, respectively, compared to FE results. Based on the obtained equations, a computer execution file was developed which is capable of calculating E when different percentages of defects are introduced to the structure. The results show that unlike single defect states, the existence of any combination of atom vacancy and atom misplacement defects causes dramatic reduction in the stiffness of carbon nanotubes. Furthermore, the role of vacancy defects in the reduction of tube’s elastic properties revealed to be more significant than misplacement defects. The results not only demonstrate that edge defects influence Young’s modulus more noticeably, but also confirm previous works showing that armchair edged structures are less vulnerable to defects, as compared to zigzag.

Performance optimization of ultra high-resolution recycling liquid chromatography

The optimization of a twin-column recycling separation process (TCRSP) for maximum resolution or maximum speed-resolution was investigated. The general optimization method was based on the construction of kinetic plots by assuming an ideal TCRSP (no efficiency loss upon recycling). For the optimization, we examined three chromatographic parameters: operation pressure (3000, 6000, 9000, and 12,000psi), column length (10, 15, and 25cm), and column inner diameter (i.d.) (2.1, 3.0, and 4.6mm). Accordingly, the highest TCRSP resolution level is expected for 25cm long columns packed with 2.5, 2.0, 1.7, and 1.6μm particles at pressures of 3000, 6000, 9000, and 12,000psi, respectively. The maximum speed-resolution performance is expected for 10cm columns packed with 3.7, 3.0, 2.6, and 2.4μm particles. 3.0mm i.d. columns are best to minimize the negative impacts of thermal and inter-column dispersion effects on the TCRSP performance. The method was illustrated for the challenging separation (selectivity factor α<1.02) of small molecules in RPLC at a maximum pressure of 6000psi using commercially available columns. Accordingly, 3.0×150mm columns packed with 2.5μm cellulose-1 Trefoil particles (chiral separation, γ-phenylbutyrolactone, α=1.01, efficiency N=4500) and 2.7μm Cortecs-C18 particles (isotope separation, α=1.02, N=14, 500) particles were found to be the most suitable columns to maximize speed-resolution performance. Further optimization of the TCRSP performance was required by reducing the inter-column sample dispersion that could cause undesirable peak tailing. A standard 2.4μL Rheodyne valve and 100μm i.d. tubes were replaced with a home-made 0.5μL low-dispersion prototype valve and 75μm i.d. perfect connection tubes. As a result, the experimental resolution factors were increased by +60% (γ-phenylbutyrolactone, 25 cycles, Rs=0.7→1.1) and +80% (deuterated benzenes, 22 cycles, Rs=1.1→2.0). Direct comparison between the experimental and the predicted TCRSP performance unambiguously demonstrated that the resolution gain was explained by the significant reduction of the peak tailing after a large number of cycles (n>20).

Various nanoparticle morphologies and surface properties of waterborne polyurethane controlled by water.

Water plays important roles in organic reactions such as polyurethane synthesis, and the aqueous solution environment affects polymer morphology and other properties. This paper focuses on the morphology and surface properties of waterborne polyurethane resulting from the organic reaction in water involving different forms (solid and liquid), temperatures and aqueous solutions. We provide evidence from TEM observations that the appearance of polyurethane nanoparticles in aqueous solutions presents diverse forms, including imperfect spheres, perfect spheres, perfect and homogenous spheres and tubes. Based on the results on FTIR, GPC, AFM and XRD experiments, we suggest that the shape of the nanoparticles may be decided by the crimp degree (i.e., the degree of polyurethane chains intertangling in the water environment) and order degree, which are determined by the molecular weight (Mn) and hydrogen bonds. Meanwhile, solid water and high-temperature water can both reduce hard segments that gather on the polyurethane film surface to reduce hydrophilic groups and produce a soft surface. Our findings show that water may play key roles in aqueous polymer formation and bring order to molecular chains.

Influence of structural imperfections—twisting and distortion—on the vibrational behavior of carbon nanotubes

Several types of carbon nanotubes in their perfect and imperfect form were simulated, and their vibrational behavior was studied by performing computational examinations with fixed-free boundary conditions. Both computational and analytical results were compared in the case of perfect tubes. Afterward, three kinds of imperfections, that is, twisting angle, z-distortion along the longitudinal axis and xy-distortion along the radial axis, were introduced to the structure of perfect carbon nanotubes, and the natural frequencies of imperfect carbon nanotubes were numerically evaluated and compared with the behavior of the perfect ones. It was concluded that the existence of any type of imperfection in the structure of carbon nanotubes leads to a lower natural frequency and, as a result, lower vibrational stability. However, this trend was more visible for the carbon nanotubes with higher chirality.

Proactive regulation of axial crushing behavior of thin-walled circular tube by gradient grooves

The progressive buckling behavior of a gradient grooved tube (GGT) designed for high temperature gas cooled reactor (HTR) is systematically studied in this paper. Based on the plastic hinge formation process, a sectionalized theoretical model is established to predict the quadratic upward trend of crushing force of GGT. The ordered and stable energy absorbing process of GGT is examined by low-speed axial impact using drop hammer test machine. The effect of proactive regulation parameters, including non-dimensional groove width W/(h0+h), groove depth h0/h and half wavelength (H+W−h)/Dh on buckling modes and force–displacement curve is determined by experiments and FE simulation. The non-dimensional groove width W/(h+h0) is determined as π/2 according to the geometry coordination of bending grooves. The non-dimensional groove depth h0/h influences local buckling behavior and the critical value 0.6 for regular bending has been determined by numerical simulation. The quadratic trend force–displacement curves of GGT can be actively controlled by (H+W−h)/Dh within a certain range less than 1.2. Free-fall impact experiments show that GGT has a better stability than perfect tube when used as an energy absorber to protect the graphite in HTR from slender control rod impact.

Atomic Structure and Mechanical Properties of Defective Carbon Nanotube (7,7)

The article presents the results of first-principle modeling of a defectless (7,7) carbon nanotube and (7,7) nanotubes containing single and double vacancy defects, as well as Stone–Wales defects. These types of defects are often found in real nanotubes and affect their properties. We have established that reliable results can be obtained by using models of more than 1.5 nm in length. It turned out that a single vacancy defect has the least influence on Young modulus, and double n type vacancy defect in the most influential. The elongation at break also depends on the defect type and is 30-60% less than for perfect tubes.

Lateral compression behaviors of thin-walled equilateral triangular tubes

The paper deals with one important topic in impact engineering - the lateral compression behavior of thin-walled tubes. To study the lateral collapse modes and energy absorption behaviors of equilateral triangular tubes, quasi-static compression experiments were carried out. Crushing modes were revealed by the experiments. Three typical crushing stages characterize the lateral deformation plateaus of equilateral triangular tubes. In simulation, perfect tubes have symmetrical crushing modes. Strengths of the tubes were correctly predicted by the competition between yielding and buckling. Based on the observed crushing modes, plastic models were proposed for each stage to predict the lateral crushing behaviors theoretically. Equilateral triangular tubes have unified energy absorbing mechanisms, including five plastic hinges and one traveling plastic hinge. Plastic models have been constructed to predict the mean crushing forces and evaluate the energy absorption efficiency of the equilateral triangular tubes.

The transformation of ZnO submicron dumbbells into perfect hexagonal tubular structures using CBD: a post treatment route

In this paper, we report the synthesis of dumbbell-shaped ZnO structures and their subsequent transformation into perfect hexagonal tubes by the extended chemical bath deposition (CBD) method, retaining all advantages such as reproducibility, simplicity, quickness and economical aspect. Well-dispersed sub-micron-sized dumbbell-shaped ZnO structures were synthesized on a SiO2/Si substrate by the CBD method. As an extension of the CBD process the synthesized ZnO dumbbells were exposed to the evaporate coming out of the chemical bath for a few minutes (simply by adjusting the height of the deposit so that it remained just above the solution) to convert them into hexagonal tubes via the dissolution process. The possible dissolution mechanism responsible for the observed conversion is discussed. The optical properties (photo-luminescence) recorded at low temperature on both the structures showed an intense, sharp excitonic peak located at ∼370 nm. The improved intensity and low FWHM of the UV peak observed in the hexagonal tubular structures assures high optical quality, and hence can be used for optoelectronic applications.

Influence of combined loading on the structural stability of carbon nanotubes

Numerous armchair and zigzag carbon nanotubes (CNTs) in their perfect and geometrically modified form were simulated and their buckling behavior was investigated through performing computational tests with different boundary conditions. Both computational and analytical results were compared in the case of perfect tubes. Then, three kinds of geometrical modifications, i.e. twisting angle, z-distortion along the longitudinal axis, and xy-distortion along the radial axis, were introduced to the configuration of perfect CNTs and the buckling behavior of geometrically modified CNTs was numerically evaluated and compared with the behavior of the perfect ones. It was shown that the first critical buckling load of both perfect armchair and zigzag CNTs increases by increasing the chiral number. In addition, it was also concluded that the existence of any type of geometrical modifications in the configuration of CNTs leads to a lower critical load and as a result, lower buckling properties. Finally, it was revealed that by increasing the length of the tubes, the critical buckling load of the CNTs reduces significantly while addition of further walls increases significantly the critical buckling load.

Structure of multi-wall carbon nanotubes: AA′ stacked graphene helices

The structure of multi-wall carbon nanotubes has been attributed previously to disordered stacking of the graphene planes. Evidence is presented that the nanotubes analyzed in this paper occur with stacked graphene layers in the sequence of AA′, where alternate graphene planes are translated by half the hexagon width. We further present proof that the crystalline materials comprise graphene helices (∼5 nm in width), rather than in the form of a perfect tube. We also show that the structural model proposed here may be a common structure for multi-wall carbon nanotubes.